Liquid dispensing devices and methods of controlling the same

ABSTRACT

The present disclosure provides a method of dispensing liquid, and a liquid dispensing device. The method and device include a controller having a multi-phase droplet ejection cycle stored thereon. The multiphase droplet ejection cycle dispenses the droplet in two stages. Advantageously, this provides highly accurate droplets of very small volumes without the formation of satellite droplets.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to devices and methods for dispensing droplets of liquids. More particularly, the present disclosure relates to liquid dispensing devices that are configured to dispense droplets of liquids while avoiding the formation of satellite droplets. Further, the present disclosure relates to methods of controlling liquid dispensing devices to dispense droplets of liquids while avoiding the formation of satellite droplets.

2. Description of the Related Art

Automatic dispensing of drops ranging in volume from a few microliters (μL) to a few tens of microliters (μL) and containing an active ingredient onto or into an edible substrate without contacting the substrate can allow pharmaceutical companies to accurately control low dose products. Additionally, liquid dosing of tablets and capsules can reduce the potential risk of operator exposure to the active ingredient.

Currently, many available devices that dispense small dosages of liquids (i.e., in the microliter range) have difficulty dispensing accurate amounts of liquid. One barrier to this is due to “satellite drops” or “satellites”, which as used in the present disclosure shall mean a very small droplet of liquid that falls after a main, larger droplet.

The elimination of satellites during the drop formation is essential to control the dose of the active ingredient and to minimize environmental contamination. Unfortunately, existing high accuracy liquid dispensing devices have been found to dispense liquids with persistent satellite droplets, particularly when dispensing solutions or suspensions that are common in the active ingredients in use in the pharmaceutical industry.

Accordingly, it has been determined by the present disclosure that there is a need for liquid dispensing devices and methods that overcome, alleviate, and/or mitigate one or more of the aforementioned and other deleterious effects of the prior art devices and methods.

SUMMARY OF THE DISCLOSURE

A liquid dispensing device is provided that is capable of delivering small, controlled volume dosages of solutions and or colloidal suspensions, such as droplets containing pharmaceutical ingredients, onto or into a solid substrate without the formation of satellite droplets.

Without wishing to be bound to any particular theory, it is believed by the present disclosure that the formation of satellite droplets can be mitigated and/or eliminated through specific, abrupt changes in the flow of the dispensed liquid. Advantageously, the liquid dispensing device of the present disclosure provides certain specific, abrupt changes in the flow of the liquid being dispensed that are sufficient to mitigate and/or eliminate the formation of satellite droplets.

A multi-phase droplet ejection profile is provided that includes a first droplet ejection phase, a dwell phase, a second droplet ejection phase, and a pump filling phase. The multi-phase ejection profile results in the formation and dispensing of a pendant droplet that is free of satellite droplets. The pump filling phase can either be a discrete step (i.e., performed alone, in series), or can occur in parallel (i.e. simultaneously) with the dwell phase. The latter of these two provides significant advantages, as discussed in greater detail below.

A liquid dispensing device is provided that includes a controller having a multi-phase droplet ejection cycle stored thereon. The multi-phase droplet ejection cycle, when executed, is configured to control a metering pump to dispense droplets of a desired volume without the formation of satellite droplets.

A liquid dispensing device is provided that includes a pump rotation controller, a servo motor, a metering pump, a volume position controller, a volume position actuator, and a motor hub body. The motor hub body converts rotary motion of the motor into a rotary and reciprocating motion of a piston in the metering pump. The volume controller selectively adjusts the stroke of reciprocation of the piston using the volume position actuator, allowing the volume of droplets ejected from the metering pump to be adjusted to a desired volume. The controller controls the speed and direction of rotation of the motor to provide a multi-phase droplet ejection cycle that dispenses droplets of the desired volume without the formation of satellite droplets.

In one embodiment, the present disclosure provides a method of dispensing fluid from a pump. The pump comprises a cylinder having an inlet port and an outlet port, and a piston within the cylinder. The piston has a linear speed along a longitudinal axis of the cylinder coupled to a rotational speed around the longitudinal axis. The method comprises the steps of: dispensing a first volume of the fluid through the outlet port to form a pendant droplet in the outlet port; dispensing a second volume of the fluid through the outlet port; and ejecting a full droplet from the outlet port. The volume of the full droplet is the sum of the first volume and the second volume. The first volume can be less than, equal to or greater than the second volume.

The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating a one-step droplet ejection profile of the prior art;

FIG. 2 is a graph illustrating a first exemplary embodiment of a multi-step droplet ejection profile according to the present disclosure;

FIG. 3 illustrates a droplet formation resulting from the ejection profile of FIG. 2, which is free of satellite droplets;

FIG. 4 is a graph illustrating an alternate exemplary embodiment of a multi-step droplet ejection profile according to the present disclosure;

FIG. 5 is a first side perspective view of an exemplary embodiment of a liquid dispensing device accordingly to the present disclosure;

FIG. 6 is a second side perspective view of the liquid dispensing device of FIG. 4;

FIG. 7 is a top perspective view of an exemplary embodiment of a metering pump according to the present disclosure;

FIG. 8 is a side perspective view of the metering pump of FIG. 7;

FIG. 9 is an exemplary embodiment of a piston from the metering pump of FIG. 7; and

FIG. 10 is a perspective view of a brushless direct current motor of the liquid dispensing device of FIG. 5.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to the drawings and, in particular, FIGS. 2 and 3, a multi-phase droplet ejection profile according to the present disclosure is shown and is generally referred to by reference numeral 10. FIG. 2 shows the velocity of the piston ejecting the droplet (discussed in greater detail below), the rotary position of the piston, the discharged volume of fluid, and the flow rate of the ejected fluid, all as function of time. Ejection profile 10 includes a first ejection phase E1, followed by a very brief dwell or stop, followed by a second ejection phase E2, and then followed by a filling phase F. During phase E2, a primary drop is formed, which contains some of the volume of a final pendant droplet 12. During ejection phase E1, the final volume is added to the primary drop formed during E2, to form and eject droplet 12. There is another dwell after filling phase F and before the next ejection phase E2, to allow the liquid dispensing device (discussed in greater detail below) to stabilize. The total cycle time of ejection profile 10 is approximately 150 milliseconds. Profile 10 of FIG. 2 stands in contrast to the prior art one-step ejection profile shown in FIG. 1. In FIG. 1, there is one, continuous ejection phase (E), after which the dispensing pump is refilled (F). While the one-step process may be simpler to operate and shorter in overall cycle time, it produces the satellite droplets discussed above. Thus, this is unacceptable, particularly for droplets on the order of a few or tens of microliters.

As shown in FIG. 2, during profile 10, the rotational speed and linear speed of the piston during phases E1, E2, and F are varied as follows. During phase E2, the rotational speed of the piston is increased steadily, and the linear speed is increased enough to force volume V2 out of the outlet port of the pump of the present disclosure. Then, during filling phase F, while the linear speed of the piston is reversed, no fluid is discharged from the outlet port, and the rotational speed is increased, so that more fluid is taken in, in the manner described below. The rotational speed is then abruptly brought to zero at the end of the stroke, which allows the droplet containing the ejected volume V2 to stabilize and wait for the next required droplet. After this brief period of stabilization, when another droplet is required, the rotational and linear speeds of the piston are increased, and volume V1 is ejected from the outlet port. Volume V1 joins volume V2 in this manner, and the sum of V2 and V1 is the volume of droplet 12. Droplet 12 is ejected at the end of phase E1, and the cycle starts again.

Advantageously, ejection profile 10 results in the formation of pendant droplet 12, which remains free of satellite droplets after droplet 12 is pinched off. There may be an aft breakoff portion 13 of droplet 12, but there is no separate satellite droplet. The total volume of droplet 12 is the sum of V1 and V2. The relative amounts of fluid in V1 and V2 can be adjusted by the user. V1 can be greater than V2, V2 can be greater than V1, or the two can be equal. For example, if during operation of device 20 (shown in FIG. 5 and discussed in greater detail below), the user notices that satellite drops are starting to form, the amount of the fluid V2 ejected during ejection phase E2 can be decreased.

Again, FIG. 2 shows both the velocity of the pump piston and the angular position thereof, as compared to the cycle time in seconds. The rate of ejection at the first ejection phase E2 is limited by the need to keep the pendant droplet 12 attached to the nozzle 16, while the filling rate of filling phase F is limited by cavitation in the ejection pump.

It has been determined by the present disclosure that the division of the ejection phase into two separate phases, E1 and E2, with the droplet ejection occurring following a rapid deceleration of the piston, at some point after the beginning of the overall ejection phase (i.e., E1 and E2) but before the end of the overall ejection phase, results in the mitigation and/or elimination of satellite droplets.

Without wishing to be bound by any particular theory, it is believed that driving the ejection profile 10 so that a sharp deceleration near the end of the drop formation process coinciding near the highest piston velocity at the center of the stroke, rather than the lower velocity at the ends of the stroke, is advantageous. Driving ejection profile 10 in this manner amplifies the effect on the fluid flow, and provides satellite free performance.

As shown in FIG. 2, the flow rate in the ejection phase E1 is non-sinusoidal when deceleration is high. For a large range of the ejection phase E1, pendant drop 12 has only one pinchoff at the aft side of the ligament, as shown in FIG. 3, with no satellite being formed. FIG. 3 shows sample droplet profiles for a suspension (upper row, time interval of 0.2 milliseconds), and for a solution (lower row, time interval 0.5 milliseconds).

In the example of ejection profile 10 of FIG. 2, the fluid sample tested was a solution having 4.2% HPC, 1.7% Silica, 0.42% Tween80, 20% Anthranquinone, and water. The solution was non-Newtonian with viscosity of about 50 mPas at shear rate of 500 per second and surface tension of 40 mN/m.

Referring to FIG. 4, an alternate embodiment of a multi-phase droplet ejection profile according to the present disclosure is shown and is generally referred to by reference numeral 14. Ejection profile 14 includes the ejection phase E1, the ejection phase E2, and the filling phase F. Ejection profile 14 also results in the formation of a pendant droplet, which remains free of satellite droplets after pinch off.

Ejection profile 14 shares the same physical basis as profile 10, but with several differences. First, the overall cycle time of profile 14 is shorter than that of profile 10 (approximately 125 milliseconds as compared to 150 milliseconds). Second, the acceleration and deceleration of the pump between the various phases have been decreased. Finally, profile 14 has eliminated the need for the pendant drop to remain on the nozzle during delays in the production cycle, minimizing nozzle fouling. Advantageously, during profile 14, the filling phase F is configured to stabilize the pendant drop 12. In ejection profile 14, as in ejection profile 10, the two ejection phases E1 and E2 are separated by filling phase F. However, in ejection profile 14, there is no dwell time in between filling phase F, and ejection phase E1, with only a small drop in the revolution speed of the piston.

As shown in FIG. 4, during profile 14, the rotational speed and linear speed of the piston during phases E1, E2, and F are varied as follows. During phase E2, the rotational speed of the piston is increased steadily driving the coupled linear distance to the end of the stroke, to force volume V2 out of the outlet port of the pump of the present disclosure. E2 of profile 14 is thus virtually identical to E2 of profile 10. Then, during filling phase F, while the linear direction of the piston is reversed and no fluid is discharged from the outlet port, the rotational speed is increased slightly, so that more fluid is taken in. Unlike in profile 10, however, after the filling phase F in profile 14, the rotational speed is only dropped slightly at the end of the stroke to enter ejection phase E1. A total volume V1 is ejected during phase E1. Thus, the major difference between profile 10 and profile 14 is that there is no significant amount of time in profile 14 during which the rotational and linear speeds of the piston are at or near zero. The pendant droplet formed by volume V2 at the end of phase E2 is stabilized during the filling phase F. Volume V1 joins volume V2 in the outlet port of the pump, and the sum of V2 and V1 is the total volume of droplet 12. Droplet 12 is ejected at the end of phase E1, and the cycle starts again.

It has been determined by the present disclosure that ejection profiles 10 and 14 are sufficient to eliminate satellite drops when dispensing delivered drops of between about 5 μL to about 30 μL. The dispensed fluids range from Newtonian to Non-Newtonian with the viscosity (in case of Non-Newtonian fluid, the dynamic viscosity) varied from between about 10 mPas to about 40 mPas and with a surface tension varied from about 22 mN/m to about 40 mN/m.

Referring now to FIGS. 5 and 6, an exemplary embodiment of a liquid dispensing device is shown and is generally represented by reference numeral 20. Advantageously, device 20 is controlled by ejection profile 10 or 14 to provide the metered dispensing of liquids, particularly high solutions or suspensions that are common in the active ingredients in use in the pharmaceutical industry, without persistent satellite droplets.

Device 20 includes a servo motor 22, a rotating and reciprocating piston metering pump 24, and a volume controller 26. As will be described in more detail below, motor 22 rotates and reciprocates the piston of metering pump 24, while volume controller 26 adjusts the stroke of the reciprocating the piston. In this manner, device 20 is configured to repeatedly dispense droplets of a desired volume without the presence of satellite droplets.

Metering pump 24 is shown with reference to FIGS. 7 through 9. Metering pump 24, commonly known as a “nutating pump”, includes a piston 28 and a motor hub body 30. Metering pump 24 uses motor hub body 30 to convert the rotational of movement of motor 22 into a rotating and reciprocating movement of piston 28.

Servo motor 22 is shown with reference to FIG. 10. It has been determined by the present disclosure that servo motor 22 provides for more accurate and repeatable control when in use with ejection profiles 10, 14.

Servo motor 22 includes a motor shaft 32 operatively coupled to motor hub body 30 so that rotation of the shaft by the motor results in rotation of the motor hub body. In the illustrated embodiment, motor shaft 32 has a key way 34 that is operatively coupled to motor hub body 30 via a key 36 shown in FIGS. 7 and 8.

Referring to FIG. 9, piston 28 includes a groove or notch 38 and a drive pin 40. Drive pin 40 is operatively engaged with a drive opening 42 of motor hub body 30, shown in FIG. 8, such that rotation of the motor hub body results in rotation of piston 28. In this manner, operation of servo motor 22 rotates piston 28 within pump 24 so that the notch 38 selectively opens and closes an inlet port (not shown) and an outlet port 25 of metering pump 24.

Referring to FIGS. 6 and 7, device 20 also reciprocates piston 28 in metering pump 24. More specifically, metering pump 24 is positioned with respect to motor hub body 30 so that piston 28 is disposed at an angle with respect to the axis of rotation of the motor hub body. In this manner, the rotation of motor hub body 30 results in drive opening 42 having an asymmetric rotation. The asymmetric rotation of opening 42 (shown more clearly in FIG. 8), when operatively coupled with drive pin 38, results in piston 28 reciprocating within metering pump 24.

As piston 28 rotates, the notch 38 is first in fluid communication with the inlet port (not shown) while the piston is withdrawn from metering pump 24 to draw fluid into the pump. As piston 28 rotates so that the notch 38 is in fluid communication with outlet port 25, the piston is forced into the metering pump 24 to force fluid from the pump. Accordingly, each single 360° rotation of piston 28 results in an intake and discharge cycle of metering pump 24. It is the controlled variation in the speed of rotation that creates the advantageous conditions.

The distance or stroke that piston 28 reciprocates can be adjusted via volume controller 26, which adjusts the angle with which piston 28 is disposed with respect to the axis of rotation of motor hub body 30. In this manner, asymmetric rotation of drive opening 42 is adjusted by volume controller 26 to provide a desired dispensing volume of each stroke of metering pump 24.

Volume controller 26 is described with reference to FIGS. 5 and 6 and includes a rotating pump mount 50, a linear actuator 52, and, in some embodiments, one or more return springs 54.

Rotating pump mount 50 is secured to device 20 to rotate about an axis of rotation A. Metering pump 24 is secured to mount 50 so that extension of linear actuator 52 causes the mount, and, thus, piston 28 in the metering pump to increase the angle with which the piston is disposed with respect to the axis of rotation of motor hub body 30. Simply stated, extension of linear actuator 52 increases the stroke of piston 28 by increasing the asymmetric rotation of drive opening 42.

Conversely, retraction of linear actuator 52 causes the mount, and, thus, piston 28 in the metering pump to decrease the angle with which the piston is disposed with respect to the axis of rotation of motor hub body 30. Simply stated, retraction of linear actuator 52 decreases the stroke of piston 28 by decreasing the asymmetric rotation of drive opening 42.

In embodiments where volume controller 26 includes return springs 54, the springs can assist actuator 52 to return mount 50 to its normal position upon retraction of the actuator.

Volume controller 26 can include a linear displacement encoder 56 to ensure that device 20 maintains a precise dispensing volume of metering pump 24 by constant monitoring of the position of mount 50.

Device 20 further includes a controller 60 in electrical communication with motor 22, actuator 52, and, when present, linear displacement encoder 56. Controller 60 is configured and programmed to control device 20 in a manner that rotates servo motor 22 along in accordance with ejection profile 10 or 14 to provide the metered dispensing of liquids without the presence of satellite droplets.

In this manner, the longitudinal stroke of piston 28 controlled to produce the output shown in profiles 10 or 14 of FIGS. 2 and 4, respectively. In profile 14 of FIG. 4, this is achieved without any significant loss in cycle time, because when the piston is momentarily stopped in a longitudinal direction, it is still rotating. That is, there is no down time during an individual dispensing cycle, during which the piston is completely stopped.

The present disclosure also contemplates a process in which piston 28 is drastically slowed or is completely stopped after the partial droplet is formed in outlet fluid port 25. Stopping piston 28 in this manner allows the droplet to stabilize as shown in ejection profile 10. Piston 28 would have a fixed dwell time, then complete the stroke to expel a complete droplet, and rotate to take in fluid for the next cycle. This method has the advantage of being easier to control, but it can be disadvantageous, as the full stop adds to the time of the dispensing cycle.

The present disclosure also contemplates another embodiment of device 20 that has two separate motors to control the liner and rotational movement of the piston. While this embodiment provides advantages in terms of more control of the dispensing operation, again, the cycle times may be adversely effected by having to operate two separate motors.

Another advantage of device 20 is provided by volume controller 26. In currently available devices, the angle of the pump mount 50 is controlled with a manually adjusted screw with a spherical tip touching the pump mount. In contrast, device 20 automates the control of the volume via volume controller 26. This allows for the operator to avoid the dispensing area for safety reasons related to exposure to the active ingredients. It also allows for the potential to provide computer controlled feedback capabilities when integrated with systems (e.g., vision-based) that measure the volume or amount of the dispensed droplets.

In some embodiments, such as one embodiment shown in FIG. 6, device 20 can have a flow-through/recirculation loop that continuously supplies fluid to circulation inlet port 44 and returns to the loop from circulation outlet port 46. This is in contrast to current “dead end” pumps, where no circulation is available. The fluid to be dispensed is run continuously through circulation ports 44 and 46, which are in communication with the inlet fluid port described above. The continuous circulation of the fluid through pump ports keeps the fluid active, preventing sedimentation or precipitation, which can be advantageous when the fluid is a suspension.

Metering pump 24 can also include one or more of a pressure sensor 62 and a turbidity sensor 64. Pressure sensor 62 can make sure that fluid is flowing at a desired rate, and turbidity or spectroscopic sensor 64 can make sure that the fluid turbidity or spectroscopic signal is within range. Sensors 62, 64, when present, can be in electrical communication with controller 60.

It should be recognized that ejection profiles 10, 14 are described herein by way of example only in use with liquid dispensing device 20 having servo motor 22, metering pump 24, and volume adjuster 26. Of course, it is contemplated by the present disclosure for ejection profiles 10, 14 to find equal use with piezoelectric metering pumps.

While the present disclosure has been described with reference to one or more particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope thereof. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure. 

What is claimed is:
 1. A method of dispensing fluid from a pump, wherein said pump comprises: a cylinder having an inlet port and an outlet port; and a piston within said cylinder, wherein said piston has a linear speed along a longitudinal axis of said cylinder and a rotational speed around said longitudinal axis, the method comprising the steps of: dispensing a first volume of the fluid through said outlet port to form a pendant droplet in said outlet port; dispensing a second volume of the fluid through said outlet port; and ejecting a full droplet from said outlet port, wherein the volume of said full droplet is the sum of said first volume and said second volume.
 2. The method of claim 1, wherein said first volume is less than said second volume.
 3. The method of claim 1 or 2, wherein said first volume is greater than said second volume.
 4. The method of claims 1 to 3, wherein said dispensing steps comprise: during a first ejection phase, controlling said linear speed and said rotational speed to increase to a first linear set point and a first rotational set point, respectively, thereby forming said pendant droplet having said first volume at said outlet port; during a filling phase, controlling said rotational speed to increase from said first rotational set point to a second rotational set point greater than said first rotational set point, and reducing said linear speed to zero, so that additional fluid is drawn through said inlet port into said cylinder; during a dwell phase, controlling each of said rotational speed and said linear speed to reduce to zero; and during a second ejection phase, increasing said rotational speed to a third rotational set point and said linear speed to a second linear set point, so that said second volume is passed through said outlet port.
 5. The method of claims 1 to 4, wherein said first rotational set point and said third rotational set point are equal.
 6. The method of claim 4, wherein said first volume is less than said second volume.
 7. The method of claim 4, wherein said first volume is greater than said second volume.
 8. The method of any of the preceding claims, wherein said dispensing steps comprise: during a first ejection phase, controlling said linear speed and said rotational speed to increase to a first linear set point and a first rotational set point, and forming said pendant droplet having said first volume at said outlet port; during a filling phase, controlling said rotational speed to increase from said first rotational set point to a second rotational set point greater than said first rotational set point, and reducing said linear speed to zero, so that additional fluid is drawn into said cylinder; and during a second ejection phase, increasing said rotational speed to a third rotational set point and said linear speed to a second linear set point, so that said second volume is passed through said outlet port.
 9. The method of claim 8, wherein said first rotational set point and said third rotational set point are equal.
 10. The method of claim 8, wherein said first volume is less than said second volume.
 11. The method of claim 8, wherein said first volume is greater than said second volume.
 12. The method of any of the proceeding claims wherein the full droplet comprises one or more pharmaceutically or cosmetically acceptable agents.
 13. The method of claim 12 wherein the full droplet is dispensed onto a receiving medium.
 14. The method of claim 13 wherein the receiving medium is a pharmaceutically acceptable tablet, or a receiving vial.
 15. A liquid dispensing device, comprising: a cylinder having an inlet port and an outlet port; a piston within said cylinder, wherein said piston has a linear speed along a longitudinal axis of said cylinder and a rotational speed around said longitudinal axis; and a controller having a multi-phase droplet ejection cycle stored thereon, said controller being operatively connected to said piston, wherein said controller controls said linear speed and said rotational speed of said piston to eject a droplet of the liquid from said outlet port in two distinct phases.
 16. The liquid dispensing device of claim 15, wherein said droplet has a droplet volume that is the sum a first volume and a second volume, and said controller controls said piston to eject said first volume during a first of said two distinct phases, and to eject a second volume during a second of said two distinct phases.
 17. The liquid dispensing device of claim 15 or 16, further comprising a linear encoder in electrical communication with said controller, wherein said controller controls a linear actuator to adjust a stroke length of said piston within said cylinder, thereby adjusting said droplet volume.
 18. The liquid dispensing device of claims 15 to 17, further comprising a circulation loop in fluid communication with said inlet port of said cylinder, wherein the fluid is circulated continuously within said circulation loop. 